Preliminary study for speciation geochemical mapping using a sequential extraction method

摘要

Sequential extraction is useful to assess the potential hazard of toxic metals and metal mobility in sediments. The extraction procedure developed by the Community Bureau of Reference (BCR) has been applied to the extraction of 51 elements from 30 stream sediments that were collected mainly for nationwide geochemical mapping in Japan. The geochemical reference samples, JSd-1, JSd-2 and JSd-3, were used to estimate the reproducibility of the elemental concentrations obtained using the BCR method. The BCR scheme is designed to extract elements in the intended phase using acetic acid (step 1), hydroxylammonium chloride (step 2), hydrogen peroxide and ammonium acetate (step 3), and hydrofluoric acid, perchloric acid, and nitric acid (step 4). The relative standard deviations of elemental concentrations in each extraction stage were generally less than + - 10 - 25 percent; the sums of elemental concentrations in respective steps (the total recoveries) ranged from 80 to 130 percent of the bulk compositions in most cases. The extraction results for respective elements showed relative uniformity among the samples originated from various geological and lithological units, suggesting the limited influence of geology on the speciation of elements. In contrast, significant differences in the extraction results were found in samples from rural and urbanized areas even though they were all from sedimentary rock areas. Samples from urban areas were characterized by a higher proportion of Co, Ni, Zn and Cd extracted in step 1 and those of Cr, Cu, and Pb in step 3, probably indicating heavy-metal contamination in their watersheds. Stream sediments near mining sites also showed a distinctive pattern in the extraction results. This study suggested that the BCR scheme is helpful for detecting the possible contamination of Cr, Ni, Cu, Zn, Cd, and Pb and exploring for mineral deposits bearing Zn, Cd and Pb.